Stimulation of tentoxin synthesis by aged-culture filtrates and continued synthesis in the presence of protein inhibitors.

Tentoxin, a cyclic tetrapeptide produced by Alternaria alternata (Fries) Keissler, induces chlorosis in certain seedling plants. It can be extracted from culture filtrates of the fungus. Tentoxin production is stimulated and increased by using a mixture of aged culture filtrates and modified Richards solution. Aged culture filtrates can be obtained from 3-week-old or older cultures of A. alternata in modified Richards solution or Pratts solution. A mixture of aged culture filtrate and fresh medium in the ratio 2:3 gives the maximal enhancement of tentoxin production. This growth system provided us with a model for studying the effects of protein synthesis inhibitors on tentoxin production. Two antibiotics which inhibit protein synthesis at the ribosomal level were tested on growth, protein synthesis, and tentoxin production in A. alternata cultures. Cycloheximide at concentrations of 500 mug/ml or emetine at concentrations of 250 mug/ml did not inhibit tentoxin synthesis, although they stopped mycelial growth and protein synthesis of the fungus at the logarithmic growth stage in the enhancement medium. These results led us to conclude that tentoxin, like certain other bioactive cyclic peptides, is synthesized by a nonribosomal peptide synthesis mechanism.

Effect of prostaglandin E1-induced elevation of cyclic AMP on glucose repression in the lactic streptococci.

Cyclic adenosine 3', 5' -monophosphate (cAMP) activity was observed in Streptococcus lactis C2, Streptococcus cremoris C10, Streptococcus diacetlactis 18-16, and Streptococcus thermophilus C3. In vitro assays of cell-free extracts obtaianed from S. lactis C2 showed that the cAMP-associated enzymes adenyl cyclase and phosphodiesterase were also present. In vitro experiments showed that prostaglandin E1 (PGE) stimulation of adenyl cyclase increased cAMP concentrations approximately fivefold, and in vivo studies showed that PGE treatment of S. lactis C2 increased intracellular cAMP concentrations twofold. Futhermore, PGE-induced elevation of intracellular cAMP levels was shown to prevent the repression of ss-D-phosphogalactoside galactohydrolase synthesis by glucose.

Antigenic variation and increase in pathogenicity in Pseudomonas aeruginosa as a result of growth on glucose or N-hexadecane as sole carbon source.

When Pseudomonas aeruginosa is grown on glucose as opposed to n-hexadecane as the sole carbon source, the antigenicity, virulence, and protein composition of the outer membrane are altered. The hydrocarbon-grown cells demonstrate a 3-log increase in virulence over the glucose-grown cells (in mice). There also appears to be an additional protein present in the outer membrane of the n-hexadecane-grown cells. This protein may contribute to the observed antigenic differences between the two cell types.

A simple transporting and maintenance medium for Mycoplasma synoviae.

A simple technique for preserving and transporting Mycoplasma synoviae, which involves suspending the cells in a 20 percent glycerol medium, is described.

Effects of the rare earth cerium on Escherichia coli.

The rare earth cerium was found to bind rapidly to Escherichia coli. Cerium inhibited oxygen uptake in the presence of glucose as well as the endogenous respiration of glucose-grown cells. For a cell concentration of 4 mg per ml, maximal inhibition was obtained at 120 mug per ml. Greater concentrations did not increase the inhibitory effect. Cerium inhibited (14)CO(2) evolution and (14)C uptake from uniformly labeled glucose. Marked changes in the distribution of (14)C incorporated into different chemical fractions of the cell were noted. The most striking changes occurred in the alcohol- and alcohol ether-soluble fractions, in which the (14)C activity was increased 5- to 20-fold in the presence of cerium.